This invention relates to a process for the nonslip finishing of surfaces, more especially packaging materials both of smooth plastics, such as films, and of other packaging materials based on paper and/or cardboard.
The nonslip finishing of various surfaces has long presented problems because the preparations in question are required to show partly conflicting properties. Thus, a preparation for the nonslip finishing of various surfaces of packaging material should not ultimately promote sticking, particularly in the form of packs because when the individual packs are separated from one another the surface, which may be printed for example, is marred. On the other hand, however, satisfactory anchorage against various movements, such as shaking and jolting, must also be guaranteed.
Interest was initially focussed on packaging materials based on cellulose, such as paper and cardboard. In their case, the preparations used for nonslip finishing were, for example, aqueous dispersions of paraffins and/or polyalkylenes which had to contain a certain amount of paraffin or polyethylene, based on the dispersion, and also incorporated certain quantities of modified natural resins and/or natural resins and also synthetic rubber. However, preparations such as these, which are known from U.S. Pat. No. 3,755,044, were used primarily for the nonslip finishing of paper or cardboard packs.
Aqueous coating compositions have also been successfully used with cellulose hydrate foil. Thus, it is known from British Pat. No. 1,072,309 that aqueous polyvinylidene chloride dispersions containing up to 3% by weight, based on the polymer, of wax and/or paraffin may be used for coating. In addition, the presence of certain nonionic emulsifiers was unavoidable.
In general, these known preparations were incapable of immobilizing packages from plastic films, for example of polyethylene, polypropylene, polyesters, atactic copolymers of ethylene with butylene and also polyamide films, during transport. In practice, this problem was solved by pretreating a thin film in such a way that it was given a rough surface by a mechanical treatment or by applying a plastic. These partially surface-treated films are known commercially as "friction film", but are expensive and thus uneconomical for many packaging applications on account of the very elaborate pretreatment involved.